JP6947052B2 - Polyester multilayer film - Google Patents

Description

The present invention relates to a multilayer film having a polyester resin composition having a furan structure. Specifically, a polyester resin A layer containing 2,5-furandicarboxylic acid units and 1,4-butanediol units as main constituent units, and a polyester resin containing terephthalic acid units and 1,4-butanediol units as main constituent units. It is a multilayer film including a B layer, and relates to a multilayer film having specific film properties.

In recent years, plant-derived polymers using biomass-derived raw materials have been developed and put into practical use as environment-friendly or environment-sustainable materials, and their needs are expected to increase in the future.

As such a polymer, for example, a poly (butylene-2,5-furandicarboxylate) composed of 2,5-furandicarboxylic acid units and 1,4-butanediol units, which are raw materials derived from biomass (hereinafter, “PBF””. A polymer is known, and Patent Documents 1 and 2 describe examples of films using the polymer.

Japanese Unexamined Patent Publication No. 2012-229395 Japanese Patent No. 05233390

Many uses are expected as a film using such a polymer. Therefore, the present inventor has tried to use the polymer as a soft packaging material, but as a result of examination by the present inventor, the performance is not good enough to use the PBF described in Patent Documents 1 and 2 alone as a soft packaging material. It turned out to be enough. More specifically, "soft packaging material" means a material for flexible packaging, and flexible packaging means flexible packaging, and the shape of the packaging is formed by putting contents such as food. It is considered that gas barrier properties and mechanical physical characteristics are required for such packaging. However, when PBF described in Patent Documents 1 and 2 is used alone as a flexible packaging material film, gas barrier performance can be obtained, but mechanical properties are required. It was found that the physical properties were insufficient and there was a concern that pinholes would easily occur.
In view of the above problems, the present invention provides an environment-friendly film using a biomass-derived raw material, which has high gas barrier properties and excellent mechanical properties, and is more suitable for flexible packaging applications. The purpose is to provide.

As a result of diligent studies to solve the above problems, the present inventor has found that the above problems can be solved by adjusting the layer structure of the film, and has completed the present invention.

That is, the gist of the present invention is as follows.
[1] A multilayer film characterized by satisfying the following (1) , (2) and (3).
(1) At least one layer is a polyester resin A layer composed of a polyester resin A having a 2,5-furandicarboxylic acid unit and a 1,4-butanediol unit as a main constituent unit. (2) At least one other layer is , A polyester resin B layer composed of a polyester resin B having a terephthalic acid unit and a 1,4-butanediol unit as a main constituent unit.
(3) The polyester resin A layer and the polyester resin B layer are directly laminated.
NS
[2] The ratio of the thickness of the polyester resin A layer to the total thickness of the multilayer film is 10 to 90.
%, The multilayer film according to [1].
[3] The multilayer film according to [1] or [2], wherein the thickness of the entire multilayer film is 5 to 1000 μm.
[ 4 ] The multilayer film according to any one of [1] to [3], wherein the tensile fracture nominal strain of the multilayer film is 100% or more.
[ 5 ] The multilayer film according to any one of [1] to [4 ], which is a multilayer film for flexible packaging materials.

It is possible to provide a multilayer film suitable for flexible packaging applications having high gas barrier properties and excellent mechanical properties.
Further, since the adhesiveness between the polyester resin A layer and the polyester resin B layer is excellent, an adhesive layer is not required between the polyester resin A layer and the polyester resin B layer, so that a smaller layer structure can be realized.

Hereinafter, typical embodiments for carrying out the present invention will be specifically described, but the present invention is not limited to the following embodiments as long as the gist of the present invention is not exceeded.

The multilayer film of the present invention includes a polyester resin A layer and a polyester resin B layer.

[Polyester resin A layer]
The polyester resin A layer of the present invention is composed of a polyester resin A having a 2,5-furandicarboxylic acid unit and a 1,4-butanediol unit as main constituent units. Specific examples thereof include poly (butylene-2,5-flange carboxylate) (hereinafter, may be referred to as “PBF”).
The polyester resin A layer has gas barrier properties and stretchability (when stretched).

Here, the "unit" means a structural unit contained in the polyester resin A derived from the monomer component used in the production of the polyester resin A, and is defined as "2,5-furandicarboxylic acid unit and 1". , 4-Butandiol unit is the main constituent unit ”means that the total of 2,5-furandicarboxylic acid unit and 1,4-butanediol unit is 50 mol% or more in all the constituent units of polyester resin A. Means that. Among them, from the viewpoint of heat resistance, it is preferably 60 mol% or more, more preferably 70 mol% or more, still more preferably 80 mol% or more, and particularly preferably 95 mol% or more.

<2,5-Flange Carboxylic Acid Unit>
The dicarboxylic acid unit constituting the polyester resin A of the present invention contains a 2,5-flangecarboxylic acid unit. When used in the production of polyester resin A, 2,5-flangecarboxylic acid and derivatives thereof can be used. Examples of the derivative of 2,5-furandicarboxylic acid include alkyl esters having 1 to 4 carbon atoms in the alkyl group, and among them, methyl ester, ethyl ester, n-propyl ester, isopropyl ester, butyl ester and the like are preferable, and more preferable. Is a methyl ester.
The ratio of the 2,5-furandicarboxylic acid unit in the dicarboxylic acid unit constituting the polyester resin A of the present invention is not particularly limited, but is preferably 50 mol% or more, more preferably 60 mol% or more, and further. It is preferably 70 mol% or more, and particularly preferably 80 mol% or more. Further, there is no particular upper limit, and 100 mol% may be used. Within these ranges, the crystallinity of the polyester resin A is maintained, and heat resistance tends to be obtained.

<Other dicarboxylic acid units>
The polyester resin A of the present invention may be copolymerized with a dicarboxylic acid unit other than the 2,5-furandicarboxylic acid unit. Preferably, the other dicarboxylic acid unit in the total dicarboxylic acid unit constituting the polyester resin A is 10 mol% or less, more preferably 5 mol% or less. Further, it is preferably 0.1 mol% or more. Within these ranges, the melting point can be slightly lowered without impairing the crystallinity. As a result, the polymerization temperature and the processing temperature can be set low, and the decomposition reaction at the time of melting and the decrease in molecular weight tend to be suppressed.
Examples of the copolymerizable dicarboxylic acid unit include aromatic dicarboxylic acid compounds, aliphatic (including alicyclic) dicarboxylic acids, and derivatives obtained by esterifying these.

<1,4-Butanediol unit>
The diol unit constituting the polyester resin A of the present invention contains 1,4-butanediol unit. When used in the production of polyester resin A, 1,4-butanediol is mainly used.

<Other diol units>
The polyester resin A of the present invention may be copolymerized with a small amount of diol units other than 1,4-butanediol. The proportion of diol units other than 1,4-butanediol in the total diol units constituting the polyester resin A is 10 mol% or less, more preferably 5 mol% or less. Further, it is preferably 0.1 mol% or more.

<Other ingredients>
In addition to the above, the polyester resin A of the present invention may contain a small amount of copolymerization component as described below. In that case, it is 10 mol% or less, preferably 5 mol% or less, in all the constituent units of the polyester resin A. When it is not more than the upper limit value, the crystallinity of the polyester resin A is maintained and heat resistance tends to be obtained. Examples of the small amount of copolymerization component include aromatic dihydroxy compounds, bisphenols, hydroxycarboxylic acids, diamines, derivatives thereof and the like.

In the polyester resin A of the present invention, a unit containing a trifunctional or higher functional group may be introduced as a copolymerization component other than the above-mentioned copolymerization component.
Examples of the compound constituting the constituent unit having a trifunctional or higher functional group include a trifunctional or higher functional alcohol; a trifunctional or higher polyvalent carboxylic acid or an anhydride thereof, an anhydrate, or an ester; and a trifunctional or higher functional compound. Included is at least one trifunctional or higher polyfunctional compound selected from the group consisting of hydroxycarboxylic acids or anhydrides, acidifieds, or esters; trifunctional or higher functional amines;

Specific examples of the trifunctional or higher functional polyhydric alcohol or the trifunctional or higher functional polyvalent carboxylic acid include glycerin, trimethylolpropane, pentaerythritol; malic acid, tartaric acid or citric acid.

<Chain extender, end sealant>
In the production of the polyester resin A of the present invention, a chain extender such as diisocyanate, diphenyl carbonate, dioxazoline, or silicic acid ester may be used. In particular, when a carbonate compound such as diphenyl carbonate is used, 20 mol% or less, preferably 10 mol% or less of these carbonate compounds may be added to all the constituents of the polyester resin A to obtain a polyester carbonate. preferable.

In the present invention, the polyester terminal group of the polyester resin A may be sealed with a carbodiimide, an epoxy compound, a monofunctional alcohol or a carboxylic acid.

<Physical characteristics of polyester resin A>
The polyester resin A of the present invention preferably has a reduced viscosity (ηred = ηsp / c; ηsp means a specific viscosity and c means a polymer concentration) of 0.8 dl / g or more. By setting this numerical range, it becomes easy to obtain the flexibility required for the flexible packaging material. Here, the reduced viscosity is obtained from the solution viscosity measured at 30 ° C. at a polyester resin concentration of 0.5 g / dl in phenol / tetrachloroethane (1: 1 weight ratio).

Further, the polyester resin A of the present invention preferably has a terminal acid value of 100 μeq / g or less. By setting this numerical range, it becomes easy to prevent a decrease in thermal stability.

Here, the terminal acid value is measured by neutralization titration. Specifically, after crushing the sample, it is dried at 140 ° C. for 15 minutes in a hot air dryer, 0.1 g of the sample cooled to room temperature in a desiccator is precisely weighed and collected in a test tube, and benzyl alcohol is collected. 3 ml is added and dissolved at 195 ° C. for 3 minutes while blowing dry nitrogen gas, and then 5 ml of chloroform is gradually added and cooled to room temperature. Add 1 to 2 drops of phenol red indicator to this solution, titrate with a benzyl alcohol solution of 0.1 N sodium hydroxide under stirring while blowing dry nitrogen gas, and finish when the color changes from yellow to red. Further, as a blank, the same operation is carried out without dissolving the sample, and the terminal acid value is calculated by the following formula (2).
Terminal acid value (μeq / g) = (ab) × 0.1 × f / w (2)
(Here, a is the amount of 0.1 N sodium hydroxide benzyl alcohol solution required for titration of the sample (μl), and b is the amount of 0.1 N sodium hydroxide benzyl alcohol required for titration in the blank. The amount of solution (μl), w is the amount of polyester resin sample (g), and f is the titer of 0.1 N sodium hydroxide solution in benzyl alcohol.)

The titer (f) of a 0.1 N sodium hydroxide solution in benzyl alcohol is determined by the following method. That is, 5 ml of methanol was collected in a test tube, and 1 to 2 drops of an ethanol solution of phenol red was added as an indicator, and 0. Titrate to the discoloration point with 0.4 ml of lN sodium hydroxide solution in benzyl alcohol, then collect and add 0.2 ml of a 0.1 N hydrochloric acid aqueous solution with a known titer as a standard solution, and add 0.1 N hydroxide again. Titrate to the discoloration point with a benzyl alcohol solution of sodium (the above operation is performed under the blowing of dry nitrogen gas). The titer (f) is calculated by the following formula (3).
Titer (f) = titer of 0.1 N hydrochloric acid aqueous solution × sampling amount of 0.1 N hydrochloric acid aqueous solution (μl) / quantification of 0.1 N sodium hydroxide solution in benzyl alcohol (μl) (3)

[How to obtain polyester resin A]
As a method for obtaining the polyester resin A of the present invention, a known method for producing a general polyester resin can be adopted. For example, the description of Japanese Patent No. 5233390 can be referred to.

[Polyester resin B layer]
The polyester resin B layer of the present invention is composed of a polyester resin B having a terephthalic acid unit and a 1,4-butanediol unit as main constituent units. Specific examples thereof include PBT resin, or a copolymerized polyester resin containing terephthalic acid, 1,4-butanediol, and polytetramethylene ether glycol as constituent units.
The polyester resin B layer has functions of flexibility and aroma retention.

The meaning of the term "unit" is the same as that defined in the polyester resin A, and "the terephthalic acid unit and the 1,4-butanediol unit are the main constituent units" means terephthalic acid. It means that the total of the unit and the 1,4-butanediol unit is 50 mol% or more in all the constituent units of the polyester resin B. Among them, from the viewpoint of crystallinity, it is preferably 60 mol% or more, more preferably 70 mol% or more, still more preferably 80 mol% or more, and particularly preferably 95 mol% or more. The preferable ratio of these units to all the units constituting the polyester resin B is also the same as the range described in the polyester resin A.

The dicarboxylic acid unit constituting the polyester resin B of the present invention contains a terephthalic acid unit. When used in the production of polyester resin B, terephthalic acid and derivatives thereof are mainly used, and examples of the terephthalic acid derivative include alkyl esters having 1 to 4 carbon atoms in an alkyl group, among which methyl esters and derivatives thereof. Ethyl ester, n-propyl ester, isopropyl ester, butyl ester and the like are preferable, and methyl ester is more preferable.

The ratio of the terephthalic acid unit to the total dicarboxylic acid unit constituting the polyester resin B of the present invention is not particularly limited, but is preferably 50 mol% or more, more preferably 60 mol% or more, still more preferably 70 mol%. The above is more preferably 80 mol% or more. Further, there is no particular upper limit, and 100 mol% may be used. Within these ranges, the crystallinity of the polyester resin B is improved, and heat resistance and good moldability tend to be obtained. The dicarboxylic acid unit other than the terephthalic acid constituting the polyester resin B is not particularly limited, and examples thereof include other dicarboxylic acid units other than the 2,5-furandicarboxylic acid unit described in the polyester resin A described above. The ratio of the other dicarboxylic acid units to the total dicarboxylic acid units constituting the polyester resin B is also not particularly limited, and the preferable range is as described for the polyester resin A.

Further, the diol unit constituting the polyester resin B of the present invention contains 1,4-butanediol unit, and may further contain polytetramethylene ether glycol unit. When used in the production of polyester resin B, 1,4-butanediol or polytetramethylene ether glycol and derivatives thereof are mainly used, and the derivatives thereof have an alkyl group having 1 to 4 carbon atoms. Alkyl esters are mentioned, and among them, methyl esters, ethyl esters, n-propyl esters, isopropyl esters, butyl esters and the like are preferable, and methyl esters are more preferable. The ratio of 1,4-butanediol units to the total diol units constituting the polyester resin B is preferably 50 mol% or more, more preferably 60 mol% or more, because of heat resistance. It is particularly preferably 70 or more.

When the polyester resin B contains a polytetramethylene ether glycol unit as a constituent unit, the ratio of the polytetramethylene ether glycol to the total diols constituting the polyester resin B is 1 mol% or more in order to impart flexibility. It is preferably 3 mol% or more, more preferably 5 mol% or more, and on the other hand, in order to maintain heat resistance, it is preferably 50 mol% or less, preferably 40 mol. It is more preferably% or less, and particularly preferably 30 mol% or less.

The polyester resin B may contain other diol units in addition to 1,4-butanediol and polytetramethylene ether glycol units. The other diol unit is not particularly limited, and examples thereof include the other diol units mentioned in the polyester resin A described above.

Further, the polyester resin B of the present invention may contain a small amount of a copolymerization component other than the above, similarly to the polyester resin A of the present invention. Further, a unit containing a trifunctional or higher functional group may be introduced as another copolymerization component other than the above-mentioned copolymerization component.

Furthermore, in the production of the polyester resin B of the present invention, a chain extender or an end-capping agent may be used in the same manner as described in the production of the polyester resin A of the present invention.

<Physical characteristics of polyester resin B>
The polyester resin B of the present invention preferably has an intrinsic viscosity in the range of 0.6 to 2.0 (dl / g). When it is at least the above lower limit value, flexibility as a flexible packaging material can be easily obtained, and when it is at least the above upper limit value, the film forming property at the time of extrusion molding tends to be good. Here, the intrinsic viscosity is measured at a temperature of 30 ° C. using a mixed solvent of 1,1,2,2-tetrachloroethane / phenol = 1/1 (weight ratio).

Further, the polyester resin B of the present invention preferably has a terminal acid value of 60 μeq / g or less. Within this numerical range, it becomes easy to prevent the thermal stability from deteriorating.

Here, the terminal acid value is measured by neutralization titration in the same manner as described for the polyester resin A. Specifically, after crushing the sample, it is dried at 140 ° C. for 15 minutes in a hot air dryer, 0.1 g of the sample cooled to room temperature in a desiccator is precisely weighed and collected in a test tube, and benzyl alcohol is collected. 3 ml is added and dissolved at 195 ° C. for 3 minutes while blowing dry nitrogen gas, and then 5 ml of chloroform is gradually added and cooled to room temperature. Add 1 to 2 drops of phenol red indicator to this solution, titrate with a benzyl alcohol solution of 0.1 N sodium hydroxide under stirring while blowing dry nitrogen gas, and finish when the color changes from yellow to red. Further, as a blank, the same operation is carried out without dissolving the sample, and the terminal acid value is calculated by the following formula (2).
Terminal acid value (μeq / g) = (ab) × 0.1 × f / w (2)
(Here, a is the amount of 0.1 N sodium hydroxide benzyl alcohol solution required for titration of the sample (μl), and b is the amount of 0.1 N sodium hydroxide benzyl alcohol required for titration in the blank. The amount of solution (μl), w is the amount of polyester resin sample (g), and f is the titer of 0.1 N sodium hydroxide solution in benzyl alcohol.)

The titer (f) of a 0.1 N sodium hydroxide solution in benzyl alcohol is determined by the following method. That is, 5 ml of methanol was collected in a test tube, and 1 to 2 drops of an ethanol solution of phenol red was added as an indicator, and 0. Titrate to the discoloration point with 0.4 ml of lN sodium hydroxide solution in benzyl alcohol, then collect and add 0.2 ml of a 0.1 N hydrochloric acid aqueous solution with a known titer as a standard solution, and add 0.1 N hydroxide again. Titrate to the discoloration point with a benzyl alcohol solution of sodium (the above operation is performed under the blowing of dry nitrogen gas). The titer (f) is calculated by the following formula (3).
Titer (f) = titer of 0.1 N hydrochloric acid aqueous solution × sampling amount of 0.1 N hydrochloric acid aqueous solution (μl) / quantification of 0.1 N sodium hydroxide solution in benzyl alcohol (μl) (3)

[How to obtain polyester resin B]
As a method for obtaining the polyester resin B of the present invention, a known method for producing a general polyester resin can be adopted. For example, the description in JP-A-2004-137455 can be referred to.
Alternatively, as another method of obtaining it, it is also possible to use a commercially available PBT resin. For example, NOVADURAN 5020 (homopolybutylene terephthalate resin, intrinsic viscosity 1.20 dl / g) manufactured by Mitsubishi Engineering Plastics Co., Ltd., or Duranex 500FP (homopolybutylene terephthalate resin, intrinsic viscosity 0.875 dl / g) manufactured by Wintech Polymer Co., Ltd. g) and the like.
Examples of commercially available products of polybutylene terephthalate-based copolymers include NOVADURAN 5505S (intrinsic viscosity 1.15 dl / g) manufactured by Mitsubishi Engineering Plastics Co., Ltd.

<Polyester resin composition>
The polyester resin A and the polyester resin B of the present invention each have various additives such as a heat stabilizer, an antioxidant, an antioxidant, a crystal nucleating agent, and a crystallization retardant, as long as their characteristics are not impaired. , Flame retardants, antistatic agents, mold release agents, lubricants, ultraviolet absorbers, colorants such as dyes and pigments, and the like may be added. Further, other thermoplastic resins may be blended.

<Multilayer film>
The multilayer film of the present invention includes a polyester resin A layer and a polyester resin B layer, and the film may or may not be stretched.
In the case of a stretched film, a stretched film can be obtained by uniaxially or biaxially stretching according to a known method. The biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching. As described above, the polyester resin A layer has functions such as gas barrier property and stretchability (when stretched), and the polyester resin B layer has functions such as flexibility and fragrance retention. It is possible to obtain a multilayer film having an extremely excellent balance between gas barrier properties and tensile properties without the need for layers.

<Physical characteristics of multilayer film>
The multilayer film of the present invention has a significantly reduced gas barrier property as compared with a film made of a polyester resin containing 2,5-furandicarboxylic acid units and 1,4-butanediol units as main constituent units. It has high tensile properties. In general, even if a multilayer film is formed with a resin layer having high tensile physical characteristics, if the resins are incompatible with each other and the adhesion is insufficient, they may be peeled off during the tensile physical characteristics test, resulting in sufficient physical characteristics. Cannot be obtained. The reason why the multilayer film of the present invention has high tensile properties without significantly lowering the gas barrier property is that the polyester resin B layer having high tensile properties is compatible with the polyester resin A layer. It is considered that this is because a stable multilayer film could be formed at the same time as showing good adhesion.

The oxygen permeability of the multilayer film of the present invention is preferably 350 cc / m2, 24 h, atm or less, more preferably 300 cc / m2, 24 h, atm or less, and 250 cc / m2, 24 h or less when converted to a thickness of 20 μm. -Atm or less is more preferable, and 150 cc / m2 / 24 h · atm or less is particularly preferable. When the oxygen permeability of the multilayer film is not more than the above upper limit value, appropriate gas barrier properties can be expected, and since it is excellent in gas barrier properties and aroma retention properties, it can be appropriately used for flexible packaging applications.

The multilayer film of the present invention preferably has a "tensile fracture nominal strain" of 100% or more. In the case of a stretched film, it means a value measured after stretching, and in the case of an unstretched film, it means a value measured with a non-stretched film. Among them, it is more preferably 110% or more, and particularly preferably 120% or more. If it is equal to or more than the above value, the packaging is flexible, pinholes are difficult to open, and it is difficult to tear, so that it can be appropriately used for flexible packaging.

The nominal strain of tensile failure can be controlled by appropriately adjusting the thickness ratio of the polyester resin A layer and the polyester resin B layer and the molecular weight of each polyester resin. The thicker the polyester resin B layer and / or the larger the molecular weight of each polyester resin, the larger the tensile fracture nominal strain tends to be.
Here, the tensile fracture nominal strain is measured by performing a tensile test according to JIS K-7127.

Further, the multilayer film of the present invention preferably has a "tensile strength" of 57 MPa or more, more preferably 60 MPa or more. When the tensile strength of the multilayer film is at least the above lower limit value, the strength as a packaging material is increased, and it becomes easy to use it for flexible packaging. The tensile strength of the multilayer film can be measured by the method described later.

The overall thickness of the multilayer film of the present invention is arbitrary, but it is preferably in the range of 5 to 1000 μm, particularly from 20 to 1000 μm, because the multilayer film has an excellent balance between flexibility and mechanical strength. It is preferably 500 μm.

The thickness of the polyester resin A layer, which is a gas barrier resin, is preferably 2.5 to 500 μm, and particularly preferably 10 to 250 μm.

The thickness of the polyester resin B layer is preferably 2.5 to 500 μm, and particularly preferably 10 to 250 μm.

Further, the thickness ratio of the polyester resin A layer to the total thickness of the multilayer film is preferably 10 to 90%. The lower limit is more preferably 20%, still more preferably 30%. By setting the value to the above lower limit or more, good gas barrier properties can be easily obtained. A more preferable upper limit value is 70%, and even more preferably 60%. If it is not more than the above upper limit value, good flexibility can be easily obtained and pinholes can be prevented from occurring.

The total thickness of the film is measured with a commercially available micrometer. On the other hand, the thicknesses of the polyester resin A layer and the polyester resin B layer can be determined by observing a transmission electron microscope (TEM) with respect to a sample obtained by cutting out a film cross section using a microtome. The thickness of the polyester resin A layer and the polyester resin B layer is not particularly limited, but can be controlled by controlling the discharge amount of each cylinder during film formation.

Further, in the multilayer film of the present invention, when the polyester resin A layer (gas barrier layer) and the polyester resin B layer are laminated, they can be directly laminated without an adhesive layer between them.

<Manufacturing method of multilayer film>
As the method for producing the multilayer film of the present invention, any method can be used as long as the multilayer film can be produced. for example,
(I) A coextrusion cast molding method in which each resin or resin composition is coextruded to obtain a multilayer film.
(Ii) A coextrusion laminating molding method in which an adhesive resin and / or polyester resin B is melt-extruded and laminated on a film constituting a layer made of polyester resin A.
(Iii) A tandem laminating molding method in which an adhesive resin and a polyester resin B are sequentially melt-extruded and laminated on a film constituting a layer made of the polyester resin A, and an anchor coating agent is used to form a film made of the polyester resin B and polyester. A method of dry laminating a film constituting a layer made of the resin A, or the like can be used.

Among the above molding methods, the coextrusion cast molding method is particularly preferable because it has excellent interlayer adhesion, requires few steps, and has high productivity. Further, the film may be uniaxially or biaxially stretched at an arbitrary rate, if necessary.

<Use of multilayer film>
The multilayer film of the present invention is useful for flexible packaging materials because it has excellent gas barrier properties and good mechanical properties. Moreover, since the multilayer film of the present invention is considered to be excellent in heat-sealing property, fragrance-retaining property, and heat resistance to retort treatment, for example, kimchi, taquan, etc. Pickles: It is considered to be suitable for packaging bags for long-term storage of foods such as curry, stew, and dumplings, and packaging bags used for retort cooking.

Further, it is suitable for a treatment bag for medical waste such as industrial waste and filth having a strong odor other than food. When the packaging bag is used, it can be easily obtained by arranging the polyester resin B layer on the outer layer of the multilayer film and binding the polyester resin B layer surface with a heat seal.

Further, as a more preferable embodiment of the present invention, the excellent adhesion between the polyester resin A layer and the polyester resin B layer eliminates the need for an adhesive layer between the polyester resin A layer and the polyester resin B layer, so that the number of layers is smaller. The configuration can be realized.
Specifically, it can be produced by a more general multilayer film molding machine instead of a special multilayer film molding machine having five or more layers. For example, the conventional five-layer structure of LLDPE / adhesive layer / EVOH / adhesive layer / PBT can be changed to a four-layer structure of LLDPE / adhesive layer / polyester resin A layer / polyester resin B layer according to the present invention. Here, LLDPE imparts heat-sealing property, EVOH and PBF impart gas barrier property, and PBT imparts strength.
(Note LLDPE = a type of polyethylene. A copolymer of ethylene and α-olefin. EVOH = a copolymer of ethylene and vinyl alcohol)

Examples will be shown below and the present invention will be described in more detail, but the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded.

<Raw materials>
[resin]
Resin 1: Prepared as follows.
In a reaction vessel equipped with a stirrer, a nitrogen inlet, a heating device, a thermometer and a decompression port, 56.07 parts by weight of dimethyl 2,5-furandicarboxylic acid and 42.51 parts by weight of 1,4-butanediol were used as raw materials. , And 1.42 parts by weight of a 1,4-butanediol solution in which 2% by weight of tetraisopropyl orthotitanium was previously dissolved was charged.
Nitrogen gas was introduced into the container while stirring the contents of the container, and the inside of the system was made into a nitrogen atmosphere by decompression substitution. Next, the reaction vessel was immersed in an oil bath at 160 ° C., and the reaction was carried out for 3 hours while stirring the inside of the system. Next, the temperature was raised to 240 ° C. over 2 hours, and then 30 minutes after the start of the temperature rise, the pressure was gradually reduced to 180 Pa or less over 1 hour and 30 minutes. Further, the polymerization was continued for 1 hour while maintaining the heating and depressurized state at this temperature, and then the polymerization was terminated to obtain a polyester resin (frangylcarboxylic acid / 1,4-butanediol polyester). The reduced viscosity of the obtained polyester resin was 1.3 dl / g, and the terminal acid value was 86 μeq / g.

Resin 2: Copolymerized polyester resin of terephthalic acid, 1,4-butanediol and polytetramethylene glycol (PTMG); a commercially available resin, NOVADURAN 5505S (intrinsic viscosity 1.15 dl / g) manufactured by Mitsubishi Engineering Plastics Co., Ltd. Using.
Resin 3: Polyamide MXD6; A commercially available resin, Lenny S6001 manufactured by Mitsubishi Gas Chemical Company, Inc. was used.

[Evaluation method]
Various evaluations were performed by the following methods.
(1) Oxygen permeability measurement Oxygen permeability measurement was performed as follows based on JIS K7162-2.
Equipment: OX-TRAN 2/21 (manufactured by MOCON)
Temperature: 23 ° C
Humidity: 50% RH
Transmission area: 50 cm ²
The smaller the oxygen permeability, the better the gas barrier property. Since the oxygen permeability is inversely proportional to the film thickness, Table 1 showing the results shows the values converted to the customarily used 20 μm thickness.

(2) Measurement of tensile physical properties (tensile strength and nominal strain at tensile failure)
The tensile physical characteristics were measured as follows based on JIS K7127.
Equipment: Precision universal testing machine Autograph AGS-H100N (manufactured by Shimadzu Corporation)
Tensile speed: 100 mm / min
Sample: The sample was punched into a dumbbell shape.

(3) Adhesion evaluation A commercially available cloth gum tape was attached to the front and back surfaces of the multilayer film and then peeled off to evaluate the adhesion. The cloth gum tape used was a cloth tape for packaging (0.2 mm thickness, 50 mm x 25 m roll) manufactured by Teraoka Seisakusho Co., Ltd.

[Example 1]
Using dried resin 1 and resin 2, a T-die film-forming machine (manufactured by Tosoku Seimitsu Kogyo Co., Ltd.) with extruder diameters of φ20 mm and φ30 mm and one T-die installed at the tip of both extruders, and a take-up roll. Film formation was performed to obtain an unstretched multilayer film in which resin 1 and resin 2 were directly laminated.
Next, various conditions are shown. The resin was dried in a hot air dryer at 100 ° C. for 8 hours. Resin 1 is put into the hopper on the φ20 mm side and resin 2 is put into the hopper on the φ30 mm side, and the resin temperature is 245 ° C. The film take-up speed was adjusted to 6.3 m / min, the roll temperature was adjusted to 20 ° C., and the total film thickness was adjusted to 90 μm. Further, the rotation speed of each extruder was adjusted so that the layer thickness ratio of the resin 1 and the resin 2 was 1: 1.

The obtained film was cut out to obtain a sample for measuring oxygen permeability. In addition, the obtained film was punched out to obtain a sample for measuring tensile physical characteristics. Using each sample, oxygen permeability measurement, tensile physical property measurement, and adhesion evaluation were performed. Table 1 shows the results of various evaluations.

[Example 2]
An unstretched film was obtained in the same manner as in Example 1 except that the rotation speed of each extruder was adjusted so that the layer thickness ratio of the resin 1 and the resin 2 was 1: 2. Subsequent sample acquisition and various evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 1]
An unstretched single-layer film of the resin 1 single layer was obtained in the same manner as in Example 1 except that the dried resin 1 was charged into the hoppers of the two extruders. The film thickness was 100 μm. Subsequent sample acquisition and various evaluations other than adhesion were performed in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 2]
An unstretched single-layer film of the resin 2 single layer was obtained in the same manner as in Example 1 except that the dried resin 2 was charged into the hoppers of the two extruders. The film thickness was 80 μm. Subsequent sample acquisition and various evaluations other than adhesion were performed in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 3]
An unstretched single-layer film of the resin 3 single layer was obtained in the same manner as in Example 1 except that the dried resin 3 was put into the hoppers of the two extruders. The film thickness was 100 μm. Subsequent sample acquisition and various evaluations other than adhesion were performed in the same manner as in Example 1. The results are shown in Table 1.

By comparison between Examples and Comparative Examples, the multilayer film of the present invention according to Examples 1 and 2 has a lower oxygen permeability than the film composed of only the polyester resin 1 of Comparative Example 1. , Each is 150 or less, and it can be seen that it has sufficient gas barrier properties for use as a flexible packaging material. Surprisingly, the multilayer film of the present invention according to Examples 1 and 2 can improve the tensile physical properties without depending on the tensile physical properties of the polyester resin 1 by using the layer made of the polyester resin 2 in combination. You can see that there is. Therefore, it can be seen that the multilayer film of the present invention is a film having few pinholes and tears, and is suitable as a film for flexible packaging materials in addition to the above-mentioned gas barrier properties. Further, since the adhesion between the polyester resin A layer and the polyester resin B layer is excellent, an adhesive layer is not required between the polyester resin A layer and the polyester resin B layer, so that a smaller layer structure can be realized.

The multilayer film of the present invention is suitable for flexible packaging applications. Specific uses for flexible packaging include packaging for vegetables, fruits, fish, meat, prepared foods, retort pouch foods, sweets, seasonings, detergents, shampoos, and the like.

Claims (5)

A multilayer film characterized by satisfying the following (1) , (2) and (3).
(1) At least one layer is a polyester resin A layer composed of a polyester resin A having a 2,5-furandicarboxylic acid unit and a 1,4-butanediol unit as main constituent units. (2) At least one other layer is , A polyester resin B layer composed of a polyester resin B having a terephthalic acid unit and a 1,4-butanediol unit as a main constituent unit. ( 3) The polyester resin A layer and the polyester resin B layer are directly laminated. Is The multilayer film according to claim 1, wherein the ratio of the thickness of the polyester resin A layer to the total thickness of the multilayer film is 10 to 90%. The multilayer film according to claim 1 or 2, wherein the thickness of the entire multilayer film is 5 to 1000 μm. Any 1 of claims 1 to 3 in which the tensile fracture nominal strain of the multilayer film is 100% or more.
The multilayer film described in the section. The multilayer film according to any one of claims 1 to 4 , which is a multilayer film for flexible packaging materials.